[FLINK-40056][docs] Support configuration anchor navigation in PyFlink

[chenzihao5]

What is the purpose of the change

Support anchor navigation for configuration in PyFlink doc, so users can easily navigate to the configuration that is referenced in the document for more details.

Brief change log

• Upgrade Sphinx to 7.4 for confval support (https://www.sphinx-doc.org/en/master/usage/domains/standard.html#directive-confval)
• Add confval tag for Python Configuration Options

Verifying this change

This change is about documentation without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Co-Authored-By: Claude Opus 4.7 (1M context)

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CI report:

• a12732c Azure: SUCCESS

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